1. Field of the Invention
The present invention relates to a hydraulic-drive work vehicle provided with a traveling stabilizer.
2. Description of the Related Art
Drive types of work vehicles such as wheeled cranes having two or more axles include a mechanical-drive type and a hydraulic-drive type. The former type may be a configuration provided with a center differential gear (hereinafter, referred to as center differential) which is a differential for distributing driving force into, for instance, front and rear axles evenly, or at a predetermined rate. The latter type may be a configuration which rotates a plurality of wheels provided at two or more axles due to torques of a plurality of hydraulic motors by using pressure oil supplied from a hydraulic pump which is driven by an engine, for instance, as disclosed in Japanese Unexamined Patent Application Publication No. 9-32045. This type provides a differential function for distributing driving force into the wheels evenly, in a similar manner to the center differential.
Incidentally, since a wheel base of this work vehicle is short and a height of the center of gravity thereof is high, the work vehicle may have a less straight-traveling stability than a passenger vehicle or truck has. This may be addressed by (1) setting restoring force of steering to a large value, for instance, by increasing a kingpin inclination or a caster angle, which are involved in wheel alignment, (2) extending the wheel base, (3) increasing a size of tires, etc.
However, in the case of (1), steering force would be increased; causing swinging ability (turning ability) to be decreased. This may be addressed by providing a power steering; resulting in the necessity of a large power assist, which causes other problems that a cost of a device is increased and a space necessary for laying out the device is increased. In addition, in a case of a hydraulic power steering, if an amount of the power assist is increased even though steering force is small, abnormal vibration is likely to be generated.
Further, according to (2), the extension of the wheel base decreases ability to access a narrow space and also ability to turn in a small diameter. Besides, it is difficult to employ (2) in consideration of the law on dimensions of the vehicle. Further, (3) also involves problems in terms of dimensions such as a width and an overall height of the vehicle. Besides, there are common problems related to the law in terms of an increase in the weight, and related to low mileage.
Meanwhile, when a front-wheel-drive vehicle is compared with a rear-wheel-drive vehicle, as in a case of a passenger vehicle, the front-wheel-drive vehicle has difficulty in turning, thereby having characteristics of good straight-traveling stability and poor swinging ability. On the other hand, the rear-wheel-drive vehicle has easiness in turning, thereby having characteristics of good swinging ability and poor straight-traveling stability. The characteristics are correlated with gripping force of the tires, and may be applied to a case of the work vehicle having the two or more axles.